Phenol alkylation has been focused on industrial application including the engineering plastic areas, grounded on its production of 2,6-xylenol, a monomer of a good heat-resisting poly-(2,6-dimethyl)phenylene oxide resin; however, catalysts employed in the reaction have not been commercially available owing to their short life time and low activity.
In this connection, studies on the develoment of highly active and selective phenol alkylating catalysts have been actively carried out; and the following catalysts have been suggested: U.S. Pat. No. 3,446,856 discloses MgO catalyst which is highly selective for ortho-alkylation of phenol at the temperature range of 475.degree. to 600.degree. C. and produces little byproducts by reducing contact time with its product, i.e., 2,6-xylenol. However, said catalyst can not be commercialized due to its low activity.
Ger. Offen 1248666 teaches phenol alkylating reaction employing aluminum catalyst; said catalyst, however, has not been applied in a practical manner, owing to its low selectivity and unstability.
On the other hand, M. Inoue et al teaches that activity of catalyst comprising metal oxides such as ZnO, Fe.sub.2 O.sub.3, Cr.sub.2 O.sub.3, TiO.sub.2 and Al.sub.2 O.sub.3 is increased in proportion to the temperature elevation in the aqueous-phase alkylation reaction[see: M. Inoue and S. Enomoto, Chem. Pharm. Bull., 24:2199 (1976)]. In the case of this catalyst, selectivity for alkylation at the ortho-position, however, is abruptly decreased at the temperature over 400.degree. C.
F. Nozaki et al reported that they had carried out vapor-phase phenol alkylating reaction employing Ca.sub.3 (PO.sub.4).sub.2 under atmospheric pressure at 350.degree. C. and 500.degree. C., where 77.7% of conversion and 88% selectivity for ortho-position methylation were obtained at the initial state and most of reactants were converted to o-cresol and 2,6-xylenol with the lapse of time.
Some other literature discloses that activities and selectivities of catalysts employed to the phenol alkylation reaction are sensitively changed according to their own acidity and basicity, and their properties can be changed by employing zeolite and mixed metal oxides. However, most of prior art catalysts have not been practically applied to industrial scale owing to their low activity, selectivity and short life time.
Accordingly, a need for the development of a highly active and selective catalyst in the vapor-phase ortho-alkylation of phenol has continued in the art.